1. Field of the Invention
This application relates to a combined or integrated spring brake modulating valve and relay valve that are contained in a single housing for an air brake system.
2. Discussion of the Art
It is common in presently available brake circuits to employ a separate modulation valve with a relay valve or with a separate quick-release valve. For example, FIG. 1 illustrates a six-by-four straight truck, i.e., a non-towing vehicle, that employs spring brakes for parking the vehicle and in which pressurized air is delivered to the spring brakes to release them during normal operation. As shown in FIG. 1, each wheel includes a brake chamber connected with a relay valve to provide air pressure to the drive axle and selectively control service application of the brakes. In addition, each wheel includes a spring brake chamber selectively supplied with air to release a large mechanical spring typically used for the park function. Air pressure to these spring brake chambers releases the mechanical spring and allows the vehicle to roll.
As is generally known in the art, if a primary circuit fails, it is desirable to take advantage of the spring brakes, yet modulate the operation of the spring brakes through a foot control valve. This is provided by the spring brake modulation valve so that the spring brakes are selectively applied through operation of the foot control valve. The secondary circuit controls the steer axle (not shown). This arrangement provides a desired braking action and modulation of the spring brakes when required.
FIG. 2 illustrates a four-by-two or six-by-two straight truck configuration. Again, a spring brake modulation valve is used in conjunction with a separate spring brake quick release valve. It is evident from a comparison of FIGS. 1 and 2 that different system configurations and plumbing arrangements are thus encountered by truck manufacturers even though the brake needs are not entirely dissimilar. Thus a need exists for simplified plumbing for the truck manufacturers that provides standardized installation across all of its vehicles. In addition, enhanced performance characteristics are always desirable.